The present invention relates to a method for producing a semiconductor device and, particularly, to an effective technology which is applied to a semiconductor device including a silicon carbide semiconductor substrate.
Since silicon carbide (SiC) has a larger band gap and an approximately one-digit larger breakdown field than those of silicon (Si), it is promising as a material for use in power devices.
As a device structure to be formed over a silicon carbide substrate, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a trench gate structure can be microfabricated and can have low on-resistance as compared with a MOSFET having a planar structure. Therefore, it is expected to be put to practical use. It is known that, to form a gate insulating film for a MOSFET, a semiconductor substrate is thermally oxidized to form a thermal oxide film which is used as a gate insulating film.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-116893) teaches that the quality of the interface of the boundary between an insulating film which includes the gate insulating film of a field effect transistor and a silicon carbide semiconductor substrate is improved by carrying out a heat treatment in a gas atmosphere accompanied by nitration after the insulating film is formed over the silicon carbide semiconductor substrate by thermal oxidation.